Conventionally, as matters to which attention must be paid to perform safety running of a vehicle, the following are listed: setting air pressure in a tire of a vehicle to a proper state and paying attention to an abraded state of the tire. For example, when the air pressure in a tire lowers, a puncture occurrence rate increases and burst occurs in high-speed running and thereby, a serious accident is caused. Therefore, a driver must always check tires.
However, even if checking tires and keeping states of the tires in preferable states, when a road is wet because of a rainy day and the friction force between the road and the tires lowers, a slip occurs when applying a brake and a vehicle moves in an unexpected direction, and thereby, an accident is caused.
To prevent an accident which is generated due to the slip or sudden acceleration or the like, an anti-lock brake system (hereafter referred to as ABS), a traction control system, and moreover a stability control system including a YAW sensor, or the like are developed.
For example, the ABS is a system for detecting the rotating state of each tire and controlling a braking force in accordance with the detection result so as to prevent each tire from becoming a lock state.
As the rotating state of each tire, it is possible to detect the rotating speed, air pressure, deflection, or the like of each tire and use the detection result for control.
As examples of the above control systems, the following are known: an automobile brake system disclosed in Japanese Patent Publication No. (Hei) 05-338528 (hereafter referred to as Patent Document 1), a brake control system disclosed in Japanese Patent Publication No. 2001-018775 (hereafter referred to as Patent Document 2), a vehicle control method and apparatus disclosed in Japanese Patent Publication No. 2001-182578 (hereafter referred to as Patent Document 3), a vehicle motion control system disclosed in Japanese Patent Publication No. 2002-137721 (hereafter referred to as Patent Document 4), and a brake system disclosed in Japanese Patent Publication No. 2002-160616 (hereafter referred to as Patent Document 5).
Patent Document 1 discloses a brake system in which a load is supplied from a vacuum tank to a vacuum booster connected with a brake, a load is supplied from a vacuum pump to the vacuum tank, the vacuum pump is driven by a pump motor and thereby, and the pump motor is controlled so that the vacuum pump operates when a state in which decelerated acceleration of an automobile having reached a predetermined value is detected by an acceleration sensor 14 to prevent a change of operation feelings during a sudden brake operation and a brake operation immediately after the sudden brake operation.
Patent Document 2 discloses a brake control system having control means for executing ABS control, in which control means is provided with: lateral acceleration estimating means for estimating lateral acceleration generated in a vehicle; and comparing-determining means for comparing estimated lateral acceleration by the lateral acceleration estimating means, estimated lateral acceleration by vehicle behavior detecting means, and detected lateral acceleration detected by a lateral acceleration sensor included in the vehicle behavior detecting means, and which determines that it is the period during normal rotation comparable with a rudder angle when the difference between the accelerations is less than a predetermined value and determines that it is the period during non-normal rotation when the difference is equal to or more than the predetermined value so as to change control at the time of determination of normal rotation and the time of non-normal rotation in ABS control.
Patent Document 3 discloses a vehicle control method and apparatus in which a control signal for adjusting the deceleration and/or acceleration of a vehicle is formed by a corresponding set value, a correction coefficient showing vehicle acceleration or vehicle deceleration generated by a tilt of a running road surface is formed and the correction coefficient is superimposed on the set value to improve the setting of vehicle deceleration and/or vehicle acceleration.
Patent Document 4 discloses a vehicle motion control unit for performing slip control for keeping a slip rate in a proper range by obtaining the slide-slip angle change speed β′ of the center-of-gravity point as an actual yawing motion state value of a vehicle having a plurality of wheels, generating a yawing moment which increases as the absolute value of the change speed β′ and decreases the absolute value of the change speed β′ by working a brake fluid pressure ΔP to any brake of right and left rear wheels when the absolute value of the change speed β′ is equal to or more than a set value β0′, continuing determination on whether slip control is necessary for a wheel to which the brake fluid pressure ΔP is worked also during the yawing moment control, and when the slip control is necessary, restraining the brake fluid pressure ΔP.
Patent Document 5 discloses a brake system having at least two sensors of an acceleration sensor for detecting the acceleration in the longitudinal direction of a vehicle, a wheel speed sensor for detecting the wheel speed of each wheel, and a brake pressure sensor for detecting a brake pressure, computing a target brake pressure in accordance with feedback from at least two sensors, computing a designated current at a designated current computing portion in accordance with the above computing result, supplying the designated current to a brake driving actuator, generating a braking force in accordance with the magnitude of the designated current and thereby, capable of restraining an output trouble even if a disturbance occurs or one sensor breaks down.
Moreover, as a method for detecting the rotating speed of a tire, as shown in FIGS. 31 and 32, a method is generally used which detects the rotating speed of a tire by a rotor 1 to be rotated with a wheel carrier and a pickup sensor 2. In the case of this method, a magnetic flux density is changed when a plurality of concave and convex portions formed on the periphery of the rotor 1 at equal intervals cross a magnetic field generated by the pickup sensor 2 and a pulsed voltage is generated in the coil of the pickup sensor 2. By detecting the pulse, it is possible to detect a rotating speed. An example of the basic principles of this method is disclosed in Japanese Patent Publication No. (Sho) 52-109981.
Patent Document 1: Japanese Patent Publication No. (Hei) 05-338528
Patent Document 2: Japanese Patent Publication No. 2001-018775
Patent Document 3: Japanese Patent Publication No. 2001-182578
Patent Document 4: Japanese Patent Publication No. 2002-137721
Patent Document 5: Japanese Patent Publication No. 2002-160616
Patent Document 6: Japanese Patent Publication No. (Sho) 52-109981